There is almost zero chance I would be able to make this work under SIP fully enabled. Code injection into system apps is something SIP tries to prevent. If there was a (theoretical) way how to circumvent it, Apple would quickly fix it in next OS update.
You can disable SIP just partially, but you still need to allow code injection and disable filesystem protection via
csrutil enable --without debug --without fs, see more details here:
I personally disabled SIP on my machine fully and I believe that I can still enjoy some benefits of SIP existence on the platform. If most people have SIP enabled on their machine then malware/spyware authors have much harder time spreading their malicious code and making money out of it, which makes it less likely they would even start developing such code for macOS platform in the first place. And that positively affects me as well although I personally have SIP disabled.
If you want to keep SIP enabled, the only other chance would be to implement whole Finder replacement app which would look & feel like Finder but with TotalFinder features baked-in. I rejected this several times because that would be too much work and I’m not sure how big the market for such thing could be. There are other file managers which are trying to serve in that space. And most importantly I personally would probably not use it. I would probably just revert to basic Finder with Terminal combo. The beauty of TotalFinder is that it was just a tiny add-on on top of normal Finder.